Effective methods for the recovery and separation of Rh, Ru, and Ir from solutions in which they are present as complex anions and which also contain typically higher concentrations of other ions represents a real need in modern technology. The current processes used are lengthy and require many processing steps. Moreover, the recoveries are generally not satisfactory. The separation of Rh and Ir from each other in these solutions also represents a real need in modern technology. As a specific example, efficient, rapid, and economical separation of Rh and Ir from each other and from concentrated HCl solutions which also contain highly concentrated base metals, Pt and Pd represents a real separation need with presently available technologies for its accomplishment being unsatisfactory. The Rh and Ir are often present at low concentrations in these solutions. Hence, it would be highly beneficial to develop a process which could selectively concentrate and recover these anions.
It is known that protonated polyamines, e.g., the ethylene diammonium cations, are capable of forming complexes with a variety of anions in single solvent, solvent extraction, and liquid membrane situations. For example, solvent extraction of precious metal chloro anions is reviewed in an article by R.A. Grant, "The Separation Chemistry of Rhodium and Iridium", in Precious Metals Recovery and Refining, Proceedings of the Precious Metals Recovery and Refining Seminar of the International Precious Metals Institute at Scottsdale, Ariz., Ed. by L. Manziek et al., Historical Publications, (1990), page 139.
Hancock et al., British Patent No. 1,530,039 issued in July 1976, "Removal of Metals from Solution"; Hancock et al., European Patent Application No. 0018102 published March 1980. "Functionalized Inorganic Oxide Products and Their Use in the 19 Removal of Heavy Metals, Transition Metals and Actinide Metals from Solution"; and Plueddeman, Canadian Patent No. 1,196,618, November 1985 "Metal Extraction from Solution and Immobilized Chelating Agents Used Therefore", describe the preparation and use of nonmacrocyclic polyalkylene-polyamine materials of both branched and unbranched form bonded to inorganic supports via strictly hydrocarbon linkages to perform ion separations. However, such materials are somewhat unstable. It is known that amine functional groups attached to silica gel, where the amine function is three carbon atoms removed from the silica gel, are not completely stable. E. P. Plueddemann, "Silane Compounds for Silylating Surfaces" Silane Surfaces and Interfaces Symposium, Ed. D. E. Leyden, Snowmass (1985), report that amine groups three atoms removed from silicon slowly lose their ability to complex copper (II). D. M. Wonnacott et al., "Hydrolytic Stability of Aminopropyl Stationary Phases Used in the Size-Exclusion Chromatography of Cationic Polymers", J. Chromatog., v. 389, pp. 103-113 (1987) and T. G. Waddell et al., "The Nature of Organosilane to Silica-Surface Bonding", JACS, v. 103, pp. 5303-5307 (1981) discuss the stability of the aminopropyl-silica gel types of materials. In the conclusion, Wonnacott et al. state that "aminoalkyl silanes which have been used extensively in the synthesis of silica-based, weak ion exchangers do not lend themselves to this type of chromatography due to their hydrolytic instability."
The preparation and use of unbranched, but highly stable macrocyclic and nonmacrocyclic polyalkylene-polyamine compounds covalently bonded to inorganic solid support to separate a wide variety of ions are described in Bradshaw et al., U.S. Pat. No. 4,952,321 issued Aug. 28, 1990, "Process of Removing and Concentrating Desired Ions from Solutions"., Bradshaw et al., U.S. Pat. No. 4,943,375 issued Jul. 24, 1990, "The Process of Separating a Selected Ion From a Plurality of Other Ions in a Multiple Ion Solution by Contacting the Solution with a Macrocyclic Ligand Bonded to Silica which Selectively Complexes with the Desired Ion"; and in Bruening et al., pending application Ser. No. 07/593,305 filed Oct. 10, 1990, "Poiytetraalkyl-ammonium and Polytriakylamine-Containing Ligands Bonded to Inorganic Supports and Processes of Using the Same for Removing and Concentrating Desired Ions from Solutions".
The potential Rh, Ir, and Ru speciation in solutions containing various complexing agents, the reduced kinetics of ligand exchange for Ir compared to Rh and Ru anionic complexes and the ability to particularly enhance the kinetics of Rh and Ru ligand exchange using elevated temperature and/or reducing agents have been alluded to in books and articles such as the aforementioned review by R. A. Grant and "Advanced Inorganic Chemistry: A Comprehensive Text", Fourth Edition, ed. by F.A. Cotton and G. Wilkinson, John Wiley and Sons, 1980, p. 912-948.
In none of the above has it been suggested or shown that highly stable polyalkylene-polyamine compounds covalently bonded to inorganic solid supports, such as silica gel, can be prepared and used to highly selectively bind Rh, Ir, and/or Ru and that these compounds allow for the Ir to be removed from the solid supported compounds after the Rh and/or Ru have been selectively eluted.
Furthermore, the preparation of highly stable branched polyalkylene-polyamine compounds covalently bonded to inorganic solid supports has also not been described.